The present invention is directed to semiconductor devices, and, more particularly, to semiconductor devices with redistribution connections between internal die contacts and external contacts exposed on an active face of the device package.
Semiconductor device packaging fulfils basic functions such as providing external electrical connections and protecting the die against mechanical and environmental stresses. Continued progress in die size reduction allows for reduced device size. However, the increased functionality and complexity of the integrated circuits require more external connections, making it difficult to reduce the overall package size.
Semiconductor devices often include multiple dies encapsulated by a molding compound. The electrical contacts for connection with external circuits are exposed at the active face of the package and connected internally with die contact pads on the semiconductor die of smaller size and spacing. The external contacts may be a ball grid array (BGA) or a land grid array (LGA), for example. Various techniques are available for connecting the exposed, external electrical contacts with the internal, die contacts.
Minimum values are specified for the size of the individual exposed, external contacts at the active face of the device and for the spacing between adjacent contacts. Such specifications necessitate a compromise between the overall size of the device active face and the number of individual electrical contacts. In wafer level packaging (WLP), a redistribution layer is built up on the wafer before adjacent devices are separated and encapsulated. The external device contacts are limited to the area of the active face of the die, and the redistribution layer acts to ‘fan in’ the contacts to make greater use of the available die face area, than if the external device contacts were aligned with the positions of the internal die contacts dictated by the morphology of the underlying integrated circuits.
In a technique known as redistributed chip packaging (RCP), a redistribution layer provides interconnections between the internal die contacts and the external exposed device contacts at the active face of the device, to route signals and power and ground connections. The redistribution layer “fans out” the die contacts, thereby offering a larger area than the active face of the die for the exposed, external device contacts and enabling larger exposed contacts to be used, with greater spacing between them.
In one RCP assembly technique, singulated dies are placed temporarily with their active faces on a substrate. The dies are encapsulated with a molding compound and then released from the substrate, forming a panel. The redistribution layer is then built up on the panel using wafer level processing techniques. The redistribution layer is built up by depositing alternating layers of insulating material and conductive material (i.e., metal layers), with vias providing connections between the metal layers. Connection with signal input/output and power and ground pads on the active faces of the dies may be made during electro-deposition of the interconnectors and vias. The devices are singulated after completion of the redistribution layer.
In another RCP production technique, a redistribution layer is prefabricated, for example using lamination operations to form alternating insulating and conducting layers, with the conducting layers connected with vias. Singulated dies are placed with their active faces on the prefabricated redistribution layer. Connection between the redistribution interconnectors and the signal input/output and power and ground internal contact pads on the active faces of the dies may be made by connector elements in the form of metal pillars or bumps, of copper for example. Connection between the metal pillars or bumps and the interconnectors of the redistribution layer may be established by fusion of solder cappings, for example. The dies on the redistribution layer are then encapsulated with a molding compound and adjacent devices are separated by singulation.
The prefabricated redistribution layer can represent a significant cost savings compared to the built-up redistribution layer but the manufacturing tolerances of positioning and dimensioning the interconnectors of the prefabricated redistribution layer are less tight, so the spacing and dimensions of the connections with the interconnectors must be larger than for a built-up redistribution layer. In both cases, it is desirable to improve the compromise between reducing the spacing of internal contact elements and increasing cost of the resulting packaged device by reducing manufacturing tolerances.